Neural mechanisms for visuomotor co-regulation in social synchronization

During social activities, people coordinate their movements by exchanging visuomotor information. Interpersonal coordination occurs from two complementary processes entailing voluntary (planned) and spontaneous (emergent) synchronization, of which neurofunctional underpinnings are unknown. We investigated the brain correlates of these two synchronization processes during an fMRI finger-tapping task. Dyads formed by IN and OUT scanner participants were instructed to reproduce a target tempo and concurrently try to synchronize to (Joint Action, JA) or resist synchronization with (Non-interactive, NI) the partners tapping, whose hand was always visible to the IN participant. Faster, slower, or equal tempi were used to induce within-dyad co-regulation. Results revealed the emergence of tempo contagion: participants tapped faster in response to the partners faster taps and vice versa for slower taps. The magnitude of such an interpersonal contagion effect was similar across conditions but associated with the activity of different neural structures. Tempo contagion correlated positively with lateral occipitotemporal cortex (LOTc) activations in the JA condition but negatively with cerebellar activations in the NI condition. This suggests visuomotor information is exploited in opposite ways depending on the task instructions: the LOTc promotes co-regulation to achieve synchronization in JA, whereas the cerebellum prevents tempo contagion to preserve individual stability in NI. This latter result is supported by a negative functional connectivity between the cerebellum and LOTc. These findings have implications for understating the interplay between planned and emergent synchronization during motor interactions.